Scanner works like input device. The scanner should put the value directly to input field.
Andrie has answered a similar question, you may check it out : https://forum.mendix.com/link/questions/100612
The barcode reader we used worked like a keyboard. When the trigger was pulled the code was read and returned as a sequence of key presses. We just used a standard text input widget and the code appeared as if someone was typing it very very quickly.
Basically: download the barcode scanner app from the AppStore and follow their documentation. It does make a difference if your app is a Hybrid mobile web application or a Native mobile application. Take the barcode-scanner.
For creation of barcodes for use during testing you can use https://mydemoversion8-sandbox.mxapps.io/p/barcode